using System;
using System.Collections.Generic;
using System.Linq;

class Program
{
    static void Main(string[] args)
    {
        var input = Console.ReadLine().Split().Select(int.Parse).ToArray();

        var dic = new Dictionary<int, int> { { 0, 0 }, { 1, 0 }, { 2, 0 }, { 3, 0 } };
        foreach (var item in input) dic[item]++;

        if (dic.ContainsValue(3))
        {
            foreach (var item in dic)
            {
                if (item.Value == 3) Console.WriteLine(item.Key);
            }
        }
        else if (dic.ContainsValue(2))
        {
            foreach (var item in dic)
            {
                if (item.Value == 1) Console.WriteLine(item.Key);
            }
        }
        else
        {
            foreach (var item in dic)
            {
                if (item.Value == 0) Console.WriteLine(item.Key);
            }
        }
    }
}